Photolithography is a well known technique in the manufacture of many kinds of devices, and finds particular use in the semiconductor industry. Photolithography is very effectively employed in the mass production of semiconductor devices. However, it suffers from a drawback in the manufacture of devices which are required in very small numbers, and in the prototyping of devices. Photolithography is a method which uses masks. The cost of making many expensive masks may be prohibitively high if a product is to be manufactured in quantities of only a few units, or if a prototype has to be modified multiple times during development. Some of the methods which have been developed to try to avoid these difficulties include device modeling and direct write technology.
Device modeling generally uses a computer to calculate, or "model," the behavior of a circuit or other device of interest. While modeling can provide important insights into the expected behavior of devices, and is generally faster and less expensive to perform than the actual fabrication of the modeled device, one obtains only a calculated result, and not an actual device of interest. Furthermore, modeling generally requires that simplifying assumptions be made to provide a tractable mathematical representation of the device under investigation. These simplifying assumptions generally cause the calculated answers to be approximations to the actual behavior of real devices.
Direct write technology generally employs a method of "writing" the patterns representing the various layers or levels of a device without a mask, by the direct illumination of a substrate with a very finely focused beam, such as an electron beam.
The patterns to be created or "written" are generally maintained in digital form in the memory of a digital computer, and are used to scan the electron beam over the surface of the substrate, and to turn the beam on and off as appropriate to generate the desired pattern. While the method can be used to produce devices, it typically suffers from the difficulties that the equipment required to carry out the process is generally more expensive than photolithography equipment, and that the process is generally slower than production using photolithography.